xattr: the unsupported features weren't linted

Signed-off-by: Vincent Batts <vbatts@hashbangbash.com>

xattr/xattr_unsupported.go

@@ -2,12 +2,20 @@
 
 package xattr
 
+// Get would return the extended attributes, but this unsupported feature
+// returns nil, nil
 func Get(path, name string) ([]byte, error) {
 	return nil, nil
 }
+
+// Set would set the extended attributes, but this unsupported feature returns
+// nil
 func Set(path, name string, value []byte) error {
 	return nil
 }
+
+// List would return the keys of extended attributes, but this unsupported
+// feature returns nil, nil
 func List(path string) ([]string, error) {
 	return nil, nil
 }